ISS schedule slips Dragon launch to May 19 – future manifest outlook

Launch of SpaceX’s first Dragon spacecraft to visit the International Space Station (ISS) has been set for a new target date of May 19, following consultations between SpaceX and NASA. The new launch date is a product of a busy schedule of ISS flight activities that Dragon needs to fit into alongside other launches and vehicles from around the globe.

Latest launch delay:

The new slip to Dragon’s launch on the COTS-2+ (C2+) mission, known in the ISS manifest as the SpX-D mission, is the latest in a series of slips, first from February 7, to late March, to April 30, to May 7, and now to May 19.

“SpaceX and NASA are nearing completion of the software assurance process, and SpaceX is submitting a request to the Cape Canaveral Air Force Station for a May 19th launch target with a backup on May 22nd,” noted the SpaceX release relating to the latest slip. “Thus far, no issues have been uncovered during this process, but with a mission of this complexity we want to be extremely diligent.”

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NASA followed with a statement by William Gerstenmaier, Associate Administrator for Human Exploration and Operations Mission Directorate (HEOMD): “After additional reviews and discussions between the SpaceX and NASA teams, we are in a position to proceed toward this important launch. The teamwork provided by these teams is phenomenal. There are a few remaining open items but we are ready to support SpaceX for its new launch date of May 19.”

The “open items”, which caused the slip from May 7, relate to ongoing software testing on the exceedingly complex Dragon capsule, which includes sophisticated on-board intelligence that allows Dragon to fly itself to the ISS without a human pilot aboard.

This latest slip however can also be partly attributed to the ISS flight manifest itself, with Dragon now being bumped to after the launch of a new crew to the ISS aboard a Russian Soyuz spacecraft.

While the latest delay will allow for more much-needed testing of the Dragon spacecraft’s complex software, it also serves to “deconflict” the Dragon mission from the planned May 15 (May 14, US time) launch of the Soyuz TMA-04M/30S spacecraft and its May 17 docking to the ISS, carrying three new members of the station’s Expedition 31 crew.

While it is understood that SpaceX, who were previously targeting May 7 for Dragon’s launch, would have preferred to launch on May 10 rather than the May 19, that date presented a problem for NASA mission planners due to its close proximity to the Soyuz TMA-04M launch, free-flight and docking.

This is due to the fact that if Dragon had launched on May 10, its berthing to the ISS would have come on May 13 – only one day prior to the May 14 (US time) launch of the Soyuz TMA-04M. This would have left only one day of mission extension time available should problems have arisen during Dragon’s rendezvous with the ISS, before the Dragon and Soyuz missions were both “on top of each other”, so to speak.

Additionally, since the C2+ mission only has launch windows available every three days – an issue related to the high propellant load for this mission, and not expected to be a feature of future Dragon missions – if the launch had been scrubbed on May 10, Dragon would have been unable to launch three days later on May 13, since this would also have put Dragon’s free-flight period “on top of” Soyuz TMA-04M’s free flight period.

NASA prefers not to have two ISS Visiting Vehicle (VV) flights occur simultaneously, due to issues such as use of communications assets, three-body rendezvous operations, and workload by ground controllers.

As such, SpaceX will now attempt to launch in the first available launch window after the May 17 docking of the Soyuz TMA-04M – which is Saturday May 19, at 4:55 AM EDT/8:55 AM GMT, marking the first ever night launch of a Falcon 9 rocket.

Assuming an on-time launch in the instantaneous launch window, Dragon would conduct the Flight Day-3 (FD-3) fly-under of the ISS on Monday May 21, for a FD-4 berthing with the ISS on Tuesday May 22. A two-week stay at the ISS would then mean an unberthing of Dragon on or around June 5, with re-entry and landing a short time later, dependant on Pacific Ocean landing site lighting (SpaceX would prefer a daylight Dragon landing).

The new launch date also means Dragon will arrive at the ISS with a six-person crew aboard the station, following the May 17 docking of Soyuz TMA-04M with Russian cosmonauts Gennady Padalka (who was aboard the ISS for the first arrival of Japan’s HTV in September 2009) and Sergey Revin, along with NASA astronaut Joe Acaba.

If Dragon had launched prior to Soyuz TMA-04M, the capture would have occurred with the three-person crew aboard the ISS, with the capture being performed by the only available USOS (United States Orbital Segment) crewmembers at that time – Don Pettit of NASA and André Kuipers of ESA.

If Dragon does not launch on the May 19, the next available launch date would be May 22. Additional launch opportunities are understood to be available through to the end of May, whereupon a solar beta angle cutout period occurs for ten days from June 3 through June 13, during which time ISS spacecraft launches and free-flights are prohibited.

Solar beta angle cutouts are periods of time where the beta angle of the Sun relative to the ISS (and any free-flying spacecraft in the ISS’ orbit) is high, meaning the Sun effectively shines on the ISS and other vehicles side-on.

This can cause issues for free-flying ISS Visiting Vehicles (VVs) related to solar array power generation, since, unlike the ISS, the solar arrays on VVs do not have beta rotation capability, meaning they cannot rotate to face the side-on Sun, and thus cannot receive enough sunlight to generate adequate power.

The free-flying spacecraft cannot orient themselves to face the Sun with their thrusters, since this would preclude them from being in the correct attitude to conduct rendezvous burns with the ISS, and could also cause thermal issues due to permanent shadowing of certain parts of the spacecraft.

Solar beta angles are not a concern for VVs that are docked or berthed to the ISS, since they can receive adequate power from the ISS via power jumpers connected through the Common Berthing Mechanism (CBM) vestibule or docking mechanism interface.

Although the solar beta angle cutout doesn’t occur until June 3, Dragon’s last launch opportunity would be around the end of May, since, if Dragon launches between the end of May and June 3, its free-flight period would occur in the beta angle cutout period, and would also leave no margin for a mission extension in the free flight period.

After the beta angle cutout period ends on June 13, Dragon would have launch opportunities on June 13 and June 16, however June 19 would not be available since an Atlas V takes the Cape Canaveral Air Force Station (CCAFS) range for its June 18 launch of NROL-38, with a few days being needed before and after that date to reconfigure the range from Falcon 9, to Atlas V, and back to Falcon 9 again.

Additional C2+ launch opportunities are understood to be available following the Atlas V launch, however on June 28 a Delta IV takes the range for the NROL-15 launch.

Looking ahead to July, the ISS flight manifest starts to present some problems for Dragon, due to the fact that the Soyuz TMA-03M undocks and lands on July 1 with Russian cosmonaut Oleg Kononenko, US astronaut Don Pettit, and ESA astronaut André Kuipers. This would leave only one USOS crewmember aboard the ISS (Joe Acaba), precluding a Dragon capture from occurring since a minimum of two USOS crewmembers are needed for any VV captures.

The USOS crew won’t be bumped back up until the July 17 docking of the Soyuz TMA-05M/31S, carrying Russian cosmonaut Yuri Malenchanko, American astronaut Sunita Williams and Japanese astronaut Aki Hoshide – the latter two of whom are USOS crewmembers.

However, following the July 17 docking of Soyuz TMA-05M, the next issue for Dragon is the July 21 launch of Japan’s H-II Transfer Vehicle-3 (HTV-3), leaving insufficient time for Dragon to launch and berth with the ISS between the 17th and 21st of July. HTV-3 will berth to the ISS on July 27, meaning Dragon will not be able to launch before then in order to avoid conflicts with the HTV-3 free flight period.

Once HTV-3 arrives at the ISS, it will occupy the berthing port planned for use by Dragon – Node 2 Nadir. Another free berthing port is available at Node 2 Zenith, however this would require HTV-3 to be relocated from Node 2 Nadir to Node 2 Zenith, as was done with HTV-2 prior to STS-133 in February, 2011.

In order to have the required reach to install a VV onto Node 2 Zenith, the Space Station Remote Manipulator System (SSRMS) must be based on the Mobile Base System (MBS) – however the SSRMS is unable to reach the VV capture point 30ft below the station from the MBS, since for that duty, it must be based on the Node 2 Power Data Grapple Fixture (PDGF).

This means that it is impossible for the SSRMS to install a captured VV directly onto Node 2 Zenith, since an SSRMS base change from the Node 2 PDGF to the MBS, to provide the required SSRMS reach to the Node 2 Zenith port, would not be possible if a VV were grappled by one end of the SSRMS (both ends of the SSRMS must be free to perform a base change).

This means that all VVs must first be installed onto Node 2 Nadir, and await an SSRMS base change from the Node 2 PDGF to the MBS, prior to being relocated to Node 2 Zenith.

Thus, an HTV-3 relocation to Node 2 Zenith, in order to free up the Node 2 Nadir port for Dragon, would not take place until at least a few days following HTV-3’s arrival at the ISS on July 27. Dragon would not be able to launch prior to an HTV-3 relocation, since a successful relocation would be a Launch Commit Criteria (LCC) for Dragon.

Additionally, Progress M-15M will undock on July 30, followed on 1st August by the Progress M-16M launch and docking on a special fast rendezvous profile. This all adds up to mean that Dragon would be very unlikely to launch to the ISS in the month of July, instead being pushed into August.

August, however, is another busy month on the ISS, complicated by a solar beta angle cutout period from August 3 to August 10, leaving insufficient time for Dragon to launch and arrive at the ISS between August 1 and August 3. An Atlas V with NASA’s RBSP mission also has the CCAFS range on August 23.

On ISS, the HTV-3 will be unberthed and released from the ISS on August 27, meaning if it had been relocated to Node 2 Zenith, it would have to be relocated back to Node 2 Nadir in the days prior to 27th. This is because, as aforementioned, the SSRMS cannot reach the VV capture point (also the release point) from the MBS, and so HTV-3 would first need to be relocated from Node 2 Zenith to Node 2 Nadir, await an SSRMS base change, prior to being unberthed and released from Node 2 Nadir.

Additionally, ISS Russian EVA-31 is planned for August 21, with the possibility for US EVA-18 in the August timeframe also. HTV-3 Exposed Pallet (EP) extraction and associated robotics operations could also complicate the picture by requiring HTV-3 to remain at Node 2 Nadir, and would also tie up use of the SSRMS required for the Dragon capture.

As such, any Dragon mission in the August timeframe would have to launch after the solar beta cutout period on August 10, and be complete a few days prior to the HTV-3 release on the August 27, in order to allow time for an SSRMS base change and HTV-3 relocation to Node 2 Nadir prior to HTV-3 being released. This would leave insufficient time to complete the planned 17 day C2+ mission, and preclude any C2+ mission extension due to on-orbit problems.

The ISS schedule would then come open for Dragon after September 3, with the next ISS flight event being the September 17 departure of Soyuz TMA-04M (which would still leave two USOS crewmembers on ISS), and with the CCAFS range free until September 20, whereupon it will go to a Delta IV for the launch of GPS II-F-3.

In summary, if Dragon does not launch between its current planned date of May 19 and late May, it will have a short window between 13th and 16th of June, another window in mid-to-late June, following which the very busy ISS flight manifest could push Dragon into the September timeframe.

While the above schedules are all notional and could be affected by delays to individual vehicles, or be re-worked in support of the C2+ mission, they show the immense challenges associated with scheduling VV missions to the ISS, with a whole fleet of international and soon commercial vehicles all needing to find their own space in the ISS manifest, in addition to their own unique launch date and range challenges.